1. Field of the Invention
The present invention relates to a paper feed device which picks up and feeds the uppermost sheet from a stack of loaded sheets of paper by suction.
2. Description of the Related Art
Paper feeding devices for picking up and feeding the uppermost or lowermost sheet from a stack of loaded sheets of paper are used in a variety of systems such as copiers or printers. General methods of picking up a single sheet from such a stack of sheets of paper use rollers or suction mechanisms. The invention relates to a method of feeding paper using a suction mechanism. The configurations of suction-based paper feeding devices of the prior art will now be explained with reference to Japanese Utility Model Law Application Disclosure HEI 2-147441 and U.S. Pat. No. 4,168,829.
As illustrated in FIGS. 10A and 10B, the device disclosed in Japanese Utility Model Law Application Disclosure HEI 2-147441 is designed so as to pick out sheet materials (photosensitive materials) 102 stored in a storage case 101 sheet from the bottom of the storage case 101, with a drum placed facing the sheet material 102 pickup port. Formed on the periphery of the drum 103 are a notched, front-end suction face 104, and a following-portion suction face 105 located upstream from the front-end suction face 104 in the direction of rotation of the drum 103. Suction pores 104a, 105a are formed through the front-end suction face 104 and the following-portion suction face 105, respectively.
The inside of the drum 103 is partitioned by a partition 108 into two compartments, a front-end suction zone 106 and a following-portion suction zone 107, with the suction pores 104a being formed communicating with the front-end suction zone 106, and the suction pores 105a being formed communicating with the following-portion suction pores 107. Individual suction means are designed so as to be connected to the front-end suction means 106 and the following-portion suction means 107. Feed rollers 109 for conveying sheet materials received from the drum 103 are arranged near the drum 3, downstream from the drum 103 in the direction of rotation thereof.
A method of feeding sheet materials using this configuration will now be described. When the front-end suction face 104 is located facing the pickup port of the storage case 101 and a vacuum is applied to the front-end suction zone 106, the front end of the sheet material 102 is sucked by the front-end suction face 104. When a vacuum is applied to the following-portion suction zone 107 while rotating the drum 103 in the direction indicated by the arrow in the figure, the following portions of the sheet material 102 are sucked by the following-portion suction face 105, thereby feeding the sheet material 102. Therefore, when the application of a vacuum to the front-end suction zone 106 is suspended when the front-end suction face 104 of the drum 103 has reached the vicinity of the feed rollers 109, the front end of the sheet material come off the drum 103, and the sheet material is forwarded to the feed rollers 109. Here, the following portions of the sheet material 102 are held on the following-portion suction face 105 under suction, and the application of a vacuum to the following-portion suction zone 106 is suspended each time the front ends have been engaged between the feed rollers 109.
As illustrated in FIG. 11, the device disclosed in U.S. Pat. No. 4,168,829, designed so as to pick up and feed sheets 112 stored in a sheet cassette 111 one by one starting with the lowermost one, is equipped with a feeder 113 for picking up the sheets near the pickup port provided at the underside of the sheet cassette 111.
The feeder 113 is shaped like a drum with suction pores 114 formed on its periphery, and a vacuum is applied to the inside of the drum so that the front end of the sheet 112 is sucked by the suction pores 114 in the vicinity of the pickup port of the sheet cassette 111. A roller 16 is placed downstream from the feeder 113 in the direction of rotation thereof. A recessed portion 113a is formed along part of the periphery of the feeder 113, with a bearing 115 being fit in the recessed portion 113a, as illustrated in the side view. The vertical position of the periphery of the bearing 115 is designed to be the same as that of the periphery of the feeder 113, with the roller 116 being in contact with the bearing 115.
An explanation will now be given regarding how the sheets 112 in the sheet cassette 112 are picked up. First, application of a vacuum to the inside of the feeder 113 is initiated when the suction pores 114 of the feeder 113 are located near and facing the pickup port of the sheet cassette 111, and the front end of each sheet 112 is sucked by the suction pores 114 on the periphery of the feeder 113. When the feeder 113 in this state is rotated in the direction indicated by the arrow in the drawing, the sheet 112 is forwarded to the position of the roller 116, at which position the sheet 112 is held between the feeder 113 (specifically, the bearing 115) and the roller 116. Therefore, even if the application of a vacuum which serves to suck the front end of the sheet is suspended at this point in time, the sheet 112 remains held between the feeder 113 and the roller 116, thereby allowing the sheet 112 to be passed to a transfer roller (not shown).
In the case of the device described in Japanese Utility Model Law Application Disclosure HEI 2-147441, the vacuums in the two suction zones 106 and 107 must be individually controlled, and this incurs the problem of complicated configuration, the problem of complicated control, the problem of ease of warp of the sheets due to the mechanism of holding the sheets by air suction only, and the problem of increased amount of air required, increased air loss and larger suction motors due to the individual control of the two zones.
On the other hand, in the case of the device described in U.S. Pat. No. 4,168,829, since the picked up sheet 112 is conveyed in the state sandwiched between the bearing 115 fit in the feeder 113 and the roller 116, the recessed portion 113a must be formed on the periphery of the feeder 113 to match the vertical position of the periphery of the bearing 115 with that of the periphery of the feeder 113, in order to prevent the sheets from warping or being otherwise deformed, which results in the complicated configuration of the feeder 113; this not only directly increases the cost, but also presents the problem of complicating even the method of fitting the bearing 115 into the feeder 113, the problem of smudging of the sheets by anti-corrosive oil, etc. on the bearing 115 because of the direct contact of the bearing 115 with the sheets, and the problem of insufficient sheet conveyance capacity due to the small, fixed area for conveying the sheets in the state sandwiched between the bearing 15 and the roller 116, since the bearing 115 is usually a specification product with fixed sizes including width.
Further, since the suction section 114 for sucking the front end of each sheet is provided on the periphery of the drum-shaped feeder 113 so that the front end of each sheet is sucked by the arc periphery, and therefore air tends to leak before and after the suction section 114 in the direction of feeding of the sheets 112 due to the stiffness of the sheets 112; additional problems include the lower suction, increased noise due to the air leakage, and increase in size of the air suction motors which is needed to secure a sufficient volume of air.